As a base film for a thermal transfer ribbon for use in a thermal transfer printer, one having a specific surface roughness (JP-A 62-299389) is known.
Of thermal transfer recording materials, demand for a sublimation-type transfer recording system has been sharply growing because the recording system is capable of outputting a high-quality full-color image with ease. The sublimation-type thermal transfer is a system in which only a thermally sublimating dye contained in a binder sublimes by heat and is absorbed into the image receiving layer of paper to which an image is transferred to form a gradation image. Since the temperature of a thermal head at the time of printing has become higher along with recent demand for higher printing speed, the quantity of heat received by a thermal transfer printer ribbon has increased. Therefore, the deformation of a film used as a base film of the ribbon has become larger, whereby an unclear printed image is produced or wrinkles are produced in a ribbon at the time of printing, or in an extreme case, printing is utterly impossible. Therefore, the improvement of printing performance has been desired.
Further, in sublimation-type thermal transfer, only a thermally sublimating dye contained in a binder sublimes by heat and is absorbed into the image receiving layer of paper to which an image is transferred to form a gradation image. In order to sublimate only the dye, high adhesion is required between the binder and the base film and, further, the adhesion must not be reduced by environmental changes and the passage of time. When the adhesion is not sufficient, the binder layer transfers to the paper and greatly impairs gradation, thereby causing an "over-transfer" phenomenon. Since a polyester film generally has highly oriented crystals, the film has such poor adhesion that an ink layer is not adhered to the polyester film at all even when it is formed on the film directly. Therefore, to improve the adhesion of the polyester film to the ink layer, a physical or chemical treatment is given to the surface of the film. However, sufficient adhesion still cannot be obtained even by the treatment.
When the ribbon is separated from an image-received sheet after printing, the ink layer may be taken away by the image-received sheet due to the delamination of the surface of the base film, which may cause abnormal transfer. Therefore, the improvement with regard to this has been desired.